In a mobile communication system, the position of a user often varies while keeping the service, and if an access network radio controller (for example, a RNC (Radio Network Controller) in 3G (3rd Generation), and a BSC (Base Station Controller) of 2G (2nd Generation)) judges that the signal coverage of the source cell where the UE (User Equipment) is located becomes weak, it will select a target cell with better signal coverage for handover.
When the source cell and the target cell belong to different Wireless Access Controllers, the process of UE relocation requires participation of a CN (Core Net). The process is as follows:
Step 101: the wireless access controller where the source cell is located triggering relocation judgment according to a measurement report sent by the UE;
Step 102: if it is found in the judging result that it needs to initiate a relocation to another wireless access controller, the source wireless access controller initiating a relocation required to the CN, wherein the relocation required message carries information of the target cell;
Step 103: the CN initiating a relocation request to the target wireless access controller;
Step 104: the target wireless access controller responding to the CN with a relocation request acknowledge message after completion of wireless resource preparation of the target cell and completion of resources preparation between the target cell and the CN;
Step 105: the CN sending a relocation command to the wireless access controller where the source cell is located;
Step 106: the wireless access controller where the source cell is located notifying the UE to initiate a relocation;
Step 107: the UE attempting to access in a new channel, and sending relocation access message to the target cell;
Step 108: the wireless access controller where the target cell is located sending a relocation detect message to notify the CN;
Step 109: the UE successfully accessing the new channel, and sending relocation complete message to the target cell;
Step 110: the target wireless access controller informing the CN of relocation complete;
Step 111: the CN notifying the wireless access controller where the source cell is located to release related resources of the UE;
Step 112: the wireless access controller where the source cell is located completing the release of the related resources and sending release complete message to the CN.
Various steps in the above process are implemented in series in terms of time, and especially during the time period from step 101 to step 106, the UE is still using the wireless resources of the source cell, so if the UE moves very fast, the wireless resource signal of the source cell rapidly deteriorates, and the probability of a relocation failure of the UE will be rather high.
In the 3GPP (3rd Generation Partnership Project) international standard protocol, there is a standard interface Iur-g between the wireless access systems, but this standard interface only supports signaling inter-transmission in the control plane.